The long-term objective of this proposal is to apply a unique and powerful "extended tethering" technology to discover novel therapeutics for the treatment of arthritis. Small molecule caspase-1 inhibitors represent a new class of arthritis therapeutics with the advantages of oral availability and decreased toxicity. Covalent tethering technology involves discovering drug-like fragments that bind to a target protein and assembling them into potent inhibitors. A protein containing a cysteine residue near a site of interest is screened against a library of sulfhydryl-containing fragments to identify fragments that bind and form a disulfide bond. In "extended tethering," the selected fragments are modified to irreversibly bind to the cysteine residue and to contain a new sulfhydryl group. These "extended tethers" allow further selection from the fragment library for additional nearby binding fragments that form a disulfide bond with the extended tether. We propose to generate and then screen five caspase-1/extended tether complexes with our fragment library to identify nearby binding fragments. Reversibly binding versions of the extended tether coupled to the selected companion fragment will be used to generate potent non-disulfide containing inhibitors. Extended tethering provides an efficient means of ligand discovery and a direct path to lead optimization since the target protein is used as a template for the construction of its own inhibitor. [unreadable] [unreadable]